We don't need a concatenation operator at all. Just use the new-improved string interpolation: "$(expression-1)$(expression-2)". In fact, since most explicit cases of concatenation are for when interpolation isn't good enough (e.g. an expression not a single variable) this will take care of most of today's uses.

When you want to make it clear that you're concatenating something, why have a small syntax? Seems to me you are asking for big syntax, to emphasize the thing. So just use join with an empty first argument (no separate cat function needed.